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SubjectRe: [PATCH] /proc/scsi/map

On Fri, 21 Jun 2002, Oliver Xymoron wrote:

> On Thu, 20 Jun 2002, Patrick Mochel wrote:
>
> > > But it was entierly behind me how to fit this
> > > in to the sheme other sd@4,0:h,raw
> > > OS-es are using. And finally how would one fit this in to the
> > > partitioning shemes? For the system aprtitions are simply
> > > block devices hanging off the corresponding block device.
> >
> > Partitions are purely logical entities on a physical disk. They have no
> > presence in the physical device tree.
>
> As I raised elsewhere in this thread, the distinction between physical and
> logical is troubling. Consider iSCSI, (aka SCSI-over-IP). It's analogous
> to SCSI-over-Fibre Channel, except that rather than using an embedded FC
> stack, it's using the kernel's IP stack. But it's every bit as much a SCSI
> disk/tape/whatever as a local device. Ergo, it ought to show up in the
> device tree so that it can be discovered in the same way. But where?

An iSCSI device is a physical device; it just doesn't reside on the local
system. We should represent the device in some physical form, since the
logical class mappings do/will assume a mapping to a physical device.

These devices are essentially children of the network via which they're
attached. When devices are discovered, I'm assuming you can derive the
network device through which you're communicating, so you can get enforce
the ancestral relationship.

You want the ancestral relationship for several reasons. You'd wouldn't
power down such a device on PM transitions or during shutdown, but you
would stop I/O transactions. The drivers for these devices should recogize
it's a remote device and handlethis. And, if you were to remove the bridge
device (the network card, etc), you want the devices behind it and their
logical mappings to go away gracefully.

Mulitpath devices, which you could easily have with multiple routes to the
same IP address, are another issue that must be addressed. It hasn't yet,
but we're getting closer...

-pat

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